1. Field of the Invention
The present invention relates to emollients, particularly emollients used in conjunction with cosmetic products (also referred to as cosmeceuticals) and pharmaceutical products that are externally applied to patients. The present invention particularly relates to the provision of oxidatively stable emollients derived from natural ingredients that provide a dry feel to the skin.
2. Background of the Art
Emollients are materials that are applied to the skin of subjects to produce softness or smoothness. They have been used for centuries in both cosmetic and pharmaceutical products. The original emollients were extracts or directly concentrated materials from plants or animals, while modern emollients also include partially synthetic (derivatives of natural products) or completely synthetic materials. The natural emollients, for the most part, have tended to provide a wet or oily feel and appearance to the skin of humans. The synthetic and partially synthetic emollients have been tailored to provide the specific type of appearance and feel desired in an end product. Even with this tailoring, there are only a few synthetic emollients that provide a highly satisfactory dry feel. Silicone emollients are the most successful dry-feel emollient.
In recent years there has been an increasing attempt in many commercial fields to use natural products from renewable sources or at least naturally derived products to both conserve resources and to reduce the pollution of the environment by materials that are not biodegradable. Silicones tend to be a class of synthetic material that are not easily degraded by the environment. The trend towards the use of natural products in cosmetics also provides motivation for manufacturers and compounders to seek alternatives to even the more successful synthetic components of their products, including silicone emollients.
In addition to the feel of an emollient, cosmetics and their ingredients must exhibit stability, both in storage and in use. The cosmetics must not deteriorate or separate in storage and use, and the individual ingredients should not decompose or otherwise undergo chemical changes that alter their desirable properties. One of the more common susceptibilities of products or components to ambient damage is from oxidation, and natural materials are clearly susceptible to oxidation, as can be commonly seen by the browning of fruit exposed to the air or the rancid smell of vegetable oils. Many foods, food additives, cosmetics, fragrances, medicaments, and colorants are well known to be subject to damaging effects from oxidation.
The most frequent means of reducing the effects of oxidation (including light amplified or stimulated oxidation) include oxygen excluding packaging (e.g., bottles, cans, oxygen impermeable polymer wraps, etc.), chemical modification of the ingredient to reduce its tendency towards oxidation while minimally altering its objective properties, and addition of antioxidants (e.g., reducing agents) to directly remove oxidative species before they oxidize the ingredient. Packaging controls are most effective where a product is to be used once, such as when a container is opened and air is introduced into the container. In this case the packaging does not provide complete protection against contact with oxygen. Chemical modification of an ingredient offers more general protection, assuming that a modification can be devised that both substantially reduces the tendency towards oxidation and also maintains the properties desired in the selection of the underlying chemical for a functional purpose, but can be an exhaustive task with no guarantees of success. The use of antioxidants offers a general approach to the problem for a wide variety of materials and fields, including even the protection of edible materials against premature oxidation. The use of antioxidants would appear to some to require little more than the appropriate selection of an antioxidant sold commercially for specific purposes to achieve a commercially viable product with a necessary level of oxidation resistance. However, antioxidants may have, and often display, unique interactions with ingredients on either a physical level (by not blending with the ingredients), on a chemical level by reacting with ingredients, or both. It is therefore necessary with some compositions, which require antioxidant protection for extensive research with no assurance of success. There are also such a wide variety of classes of antioxidants and so many variants within the classes that a search for an appropriate antioxidant is a highly problematic search, and the desire for the best antioxidant assures a time consuming process.
Among the more common classes of antioxidants are free-radical terminators, particularly those with available hydrogens from phenolic hydroxyl groups. Within that single class are the subclasses of butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT), hydroquinones (such as tertiary-butylhydroquinones, propyl gallate, and tocopherols). Reducing agents, or oxygen scavengers, encompass another class of antioxidants and include ascorbic acid (vitamin C) and its derivatives (such as esters of ascorbic acid, ascorbyl esters such as ascorbyl palmitate); sulfites (such as sulfur sulfite, alkali metal sulfites, and bisulfites, including alkali metal bisulfites); glucose oxidase (including catalase); erythorbic acid and its derivatives. Chelating agents comprise another class of materials that have been used to address problems with oxidation and include citric acid and its derivatives, polyphosphates, and aminopolycarboxylic acids (such as ethylenediaminetetraacetic acid (EDTA)). There are additional antioxidant classes with less general areas of use.
U.S. Pat. No. 5,552,167, issued Sep. 3, 1996, describes a rice bran oil antioxidant, wherein high linolenic edible oils such as soybean oil and canola are stabilized by blending the oils with rice bran oil in amounts effective to render the oils stable to oxidation. Preferred embodiments employ from about 0.5% to about 10%, more narrowly from about 2% to about 5%, by weight rice bran oil specially processed to retain unsaponifiable matter. In one embodiment, physically refined rice bran oil is used. The natural stabilized oil is especially useful as a spray oil for crackers, nuts, chips, and other snack products.
U.S. Pat. No 5,876,736, issued Mar. 2, 1999, describes a cosmetic makeup composition containing at least one liposome-encapsulated or phospholipid-encapsulated moisturizer or re-hydrating agent and, preferably, an encapsulated blend of moisturizing/re-hydrating ingredients. For example, the encapsulated moisturizer or re-hydrating agent may be D,L-panthenol, D-panthenol, vitamin A palmitate, vitamin E acetate, methylsilanetriol mannuronate, natural oils such as tallow oil, macadamia nut oil, borage oil, evening primrose oil, kukui nut oil, rice bran oil, tea tree oil, a medium chain fatty acid ester of glycerol, such as glycerol triheptanoate, glyceryl trioctanoate, mineral water, silicones, and silicone derivatives. Mixtures of two or more of these ingredients may be used. A preferred moisturizer is a liposome vesicle containing D-panthenol.
U.S. Pat. No. 5,902,590, issued May 11, 1999, describes cosmetic and/or pharmaceutical formulations with increased viscosity and improved stability in storage which are distinguished by a content of selected esters of oligoglycerols with fatty acids as emulsifiers. This reference asserts that emulsifiers are required for the permanent homogeneous mixing of substances that would otherwise be immiscible with one another. Esters of fatty acids with polyhydric alcohols, for example pentaerythritol, dipentaerythritol, or self-condensation products of glycerol, so-called technical oligoglycerol mixtures, are often used for this purpose in cosmetic and pharmaceutical formulations, for example for the production of cremes and notions. A review of this subject by G. Schuster and H. Pospischil was published in Arztl. Kosmetol., 11, 30-37 (1981).
The use of polyglycerol esters as o/w emulsifiers for cosmetic formulations is described, for example, in J. Soc. Cosmet. Chem. 28, 733-740 (1977) and in Fette, Seifen, Anstrichmittel 88, 101-106 (1986). In addition, the use of selected polyglycerol fatty acid esters as cosmetic emulsifiers is claimed in DE-A1 40 05 819 and in DE-A1 40 23 593 (BASF). However, in cases where the esters based on unsaturated or saturated fatty acids mentioned in these documents are used, it has been found that the resulting emulsions are not always sufficiently stable in storage and/or are low in viscosity, i.e. have a viscosity which is not sufficiently high, so that problem-free dosing is difficult. The invention of that reference relates to cosmetic and/or pharmaceutical formulations that are characterized in that they contain statistical monoesters of technical triglycerol with saturated C.sub.16 -C.sub.18 fatty acids as emulsifiers, the monoester content being from 30 to 50% by weight. It was asserted that it was surprising that the degree of self-condensation of the oligoglycerols in conjunction with the nature of the fatty acid and the percentage content of monoesters has a critical bearing on the properties of the resulting emulsifiers. That invention includes in particular the observation that the establishment of a percentage monoester content of 30 to 50% in the emulsifiers according to the invention leads to a significant improvement in storability and viscosity compared with otherwise known products of the prior art.